High-pressure phase of cold-compressed bulk graphite and graphene nanoplatelets
Ilias Efthimiopoulos, Elissaios Stavrou, Koichiro Umemoto, Sathish Mayanna, Antonius Torode, Jesse S. Smith, Stella Chariton, Vitali B. Prakapenka, Alexander F. Goncharov, Yuejian Wang
Abstract
We have studied the high-pressure vibrational and structural behavior of bulk graphite and graphene nanoplatelets at room temperature by means of high-pressure Raman spectroscopic and x-ray diffraction probes. We have detected a clear pressure-induced structural transition in both materials, evidenced by the appearance of new Bragg peaks and Raman features, deviating from the starting hexagonal graphitic structure. The high-pressure phase is identified as a partially disordered orthorhombic structure, consisting of mixed $s{p}^{2}$- and $s{p}^{3}$-type bonding. Our experimental findings serve as direct evidence for the existence of a metastable transient modification in cold compressed carbon, lying between the $s{p}^{2}$-type graphite and ${sp}^{3}$-type diamond allotropes.